Radio telecommunications service is presently provided on a cellular basis to mobile telephones which communicate to a base station within each cellular area. A North American TDMA digital cellular network standard IS54 has been proposed, which is primarily intended to carry digitized voice traffic instead of analog voice traffic between the mobile radio telephone stations and the base stations. The standard seeks to conserve the scarce resource of radio bandwidth in the cellular networks by transmitting telephone speech as digitized voice packets in the time slots of a TDMAtime frame. The new proposed IS54 standard will provide for a 3:1 capacity gain over the current conventional Amps standard, which is documented in the TIA Standard IS54. The Amps-D and IS54 terminology refers to the same air radio interface.
The technique described in the foregoing patent application "Method and Apparatus for Exploitation of Voice Inactivity to Increase the Capacity of a Time Division Multiple Access Radio Communication System" will avoid allocating bandwidth to the pauses which occur in speech. The system referred to herein as the E-TDMA.RTM. allots bandwidth to accommodate each speech burst. Each time a speech burst occurs, a request to allocate a time slot is generated and a time slot in the reverse data frame is assigned for carrying the digitized speech burst.
To implement the foregoing protocol of assigning time slots to mobile stations when a digitized speech burst is created, the protocol envisions a time division multiplex access system having a forward TDMA frame from the base station to each of the mobile stations and a reverse TDMA frame of data packets from the mobile stations to the base station. The time slots of the reverse TDMA frame are assigned by the base station as allocation requests are received from each mobile station which has created a digitized voice packet to transmit. Thus, the idle time represented by a speech pause does not receive any allocated bandwidth which would go unused.
The system described in the aforementioned co-pending patent application provides a base station which manages a pool of transmission channels comprising a plurality of different carrier frequencies, each of which are modulated with forward and reverse TDMA frames. The base station will manage the incoming data packets received from the PSTN as well as make the dynamic, on the fly reverse frame data slot assignments to each mobile station having a speech packet to transmit.
The assignment of time slots in the reverse data frame results when a mobile station having a data packet issues a channel allocation request in a control slot of the reverse TDMA frame. The base station, once obtaining the allocation request, will identify an available time slot within the subsequent reverse data frame, and communicate the identity of that time slot to the requesting mobile in the forward data frame. The requesting mobile station can then transmit the digitized voice packet in the allotted time slot.
In order to preserve the speech quality, the packet assignment must not incur any significant delay such that the time between the transmission of voice packets is delayed, indicating pauses of a greater length than that which were actually produced in the original speech. The system must have an adequate number of time slots to service both very light traffic from the mobile to the base station, as well as very heavy traffic.
In the foregoing North American TDMA Digital Cellular Network Standard IS54, there is also a proposal to incorporate a data mode such that a mobile or remote data terminal can use any available time slots in the reverse frame.
The introduction of data traffic in an essentially voice telecommunications system requires a protocol which will take into account the needs of both services. Data packets originating from a data terminal are not as time-sensitive to delays as are speech packets. Thus, it is possible to provide a lesser priority to data station data packets than voice station data packets.
Further, in order to have a system of mixed digital voice packet transmission and digital data transmission, the system must be adaptable to different traffic loads on the network. As channel traffic increases, the system must equitably distribute bandwidth to contending data stations, while still maintaining enough bandwidth for the higher priority voice stations to preserve the voice quality.